The proposal is a basic study of the kinetics and thermodynamics of serine biosynthesis using both in vitro and in vivo approaches. The project may be sub-divided into three areas: 1) the purification, physical-chemical characterization, and detailed kinetic analysis under physiological conditions of the forward and reverse reactions of the enzymes of the phosphorylated pathway of serine synthesis (D-3-phosphoglycerate dehydrogenase, and phosphoserine aminotransferase, and phosphoserine phosphatase); 2) the determination of the equilibrium constants under physiological conditions for two reactions of the non-phosphorylated pathway of serine synthesis (D-glycerate dehydrogenase and serinepyruvate aminotransferase), the equilibrium constants of the reactions of the phosphorylated pathway and those remaining in the non-phosphorylated pathway having already been completed in our laboratory, and 3) the development of an animal model for the study of serine biosynthesis in vitro including determination in rapidly frozen tissue of key intermediates and effector levels of the pathways of serine synthesis by a variety of enzymatic spectrophotometric and fluorometric procedures.